Method for stopping a reaction during the production of aromatic amines from nitroaromatics

Abstract

The present invention relates to a method for producing aromatic amines by the hydrogenation of aromatic nitro compounds. This method supplies aromatic nitro compounds and hydrogen to a reactor and contacts them with a hydrogenation catalyst; and stops the supply of aromatic nitro compounds and hydrogen to the reactor. The supply of aromatic nitro compounds and hydrogen to the reactor is stopped to ensure safe shutdown of the reactor.

What is claimed is: 
     
       1. A process for preparing aromatic amines by hydrogenation of aromatic nitro compounds, which comprises:
 A) introducing aromatic nitro compounds and hydrogen into a reactor and contacting with a hydrogenation catalyst; 
 B) stopping the introduction of aromatic nitro compounds and hydrogen into said reactor; 
 characterized in that step B) is carried out by 
 B1) firstly stopping the introduction of aromatic nitro compounds into said reactor so that aromatic nitro compounds present in said reactor and/or in plant parts fluidically connected upstream to said reactor react with said hydrogen which continues to be fed into said reactor, and 
 B2) subsequently stopping the introduction of hydrogen after a predetermined time and/or after the concentration of aromatic nitro compounds in the gas stream entering the reactor falls below a predetermined value. 
 
     
     
       2. The process as claimed in  claim 1 , wherein said hydrogen gas is circulated through said reactor in step B1). 
     
     
       3. The process as claimed in  claim 1 , wherein the amount of aromatic nitro compounds and hydrogen is reduced in each case to from ≧1% by mass to ≦40% by mass of the amount introduced previously in step A) before step B). 
     
     
       4. The process as claimed in  claim 1 , wherein said reactor is filled with an inert gas after step B). 
     
     
       5. The process as claimed in  claim 1 , wherein step A) is carried out isothermally. 
     
     
       6. The process as claimed in  claim 1 , wherein the molar ratio of hydrogen to nitro groups of said aromatic nitro compounds in step A) is from ≧3:1 to ≦6:1. 
     
     
       7. The process as claimed in  claim 1 , wherein said predetermined time in step B2) is ≧1 hour. 
     
     
       8. The process as claimed in  claim 1 , wherein the predetermined concentration of aromatic nitro compounds in said gas stream entering said reactor in step B2) is less than 1000 ppm. 
     
     
       9. The process as claimed in  claim 1 , wherein aromatic nitro compounds having the general formula (I): 
       
         
           
           
               
               
           
         
       
       in which:
 R1 and R2 are each, independently of one another, hydrogen, methyl or ethyl, with the proviso that R2 can also be NO 2 , are used in step A). 
 
     
     
       10. The process as claimed in  claim 1 , wherein said catalyst is arranged in a fixed catalyst bed in said reactor.